New discoveries of the way plants transport important substances across their biological membranes to resist toxic metals and pests, increase salt and drought tolerance, control water loss and store sugar can have profound implications for increasing the supply of food and energy for our rapidly growing global population.
That’s the conclusion of 12 leading plant biologists from around the world whose laboratories together with others have recently discovered important properties of plant transport proteins that, collectively, could have a profound impact on global agriculture. They report in the May 2nd issue of the journal Nature that the application of their findings could help the world meet its increasing demand for safe and sustainable food and fuel as the global population grows from seven billion people to an estimated nine billion by 2050.
These membrane transporters are a class of specialized proteins that plants use to take up nutrients but also toxic metals from the soil and mediate resistance toxic substances like heavy metals, salt and aluminum,” said Julian Schroeder, senior author and professor of biology at UC San Diego who brought together 11 other scientists from Australia, Japan, Mexico, Taiwan, the U.S. and the U.K. to collaborate on a paper describing how their discoveries collectively could be used to enhance safe and sustainable food and fuel production.
Schroeder is one of the principle investigators in UCSD's large, multidisciplinary Superfund Research Center (SRC) funded by the National Institute of Environmental Health Sciences (2012-2017). The SRC has a twofold objective: (1) generate new perspectives on the molecular and genetic basis of the biological effects of toxicant exposure, and (2) develop new models for the detection and bioremediation of chemical toxicants found at Superfund sites. For the SRC, one of Schroeder’s aims is to better understand the potential of using plants for bioremediation of arsenic and cadmium.
The uptake of heavy metals into plants via the root system and accumulation of heavy metals in plant shoots could provide a cost effective approach for toxic metal removal and remediation of heavy metal-laden soils and waters. Schroeder’s lab has identified key mechanisms by which plants accumulate, transport and detoxify heavy metals by combining genomic, genetic, biochemical and physiological approaches. Understanding the control of heavy metal accumulation and distribution in roots and shoots is critical for engineering of plants for bioremediation and for reduced accumulation in edible tissues of crop plants. Schroeder and his lab members are working closely with the SRC’s Research Translation Core and Community Engagement Core to share research findings for their potential in addressing these acute problems.
Schroeder is also co-director of UC San Diego’s new Center for Food and Fuel for the 21st Century, a research entity designed to apply basic research on plants to sustainable food and biofuel production, said many of the recent discoveries in his and other laboratories around the world had previously been “under the radar”—known only to a small group of plant biologists—but that by disseminating these findings widely, the biologists hoped to educate policy makers and speed the needed basic research advances and eventual application of their discoveries.
“Of the present global population of seven billion people, almost one billion are undernourished and lack sufficient protein and carbohydrates in their diets,” the biologists write in their paper. “An additional billion people are malnourished because their diets lack required micronutrients such as iron [and] zinc”. These dietary deficiencies have an enormous negative impact on global health resulting in increased susceptibility to infection and diseases, as well as increasing the risk of significant mental impairment. During the next four decades, an expected additional two billion humans will require nutritious food. Along with growing urbanization, increased demand for protein in developing countries coupled with impending climate change and population growth will impose further pressures on agricultural production.”
“Simply increasing inorganic fertilizer use and water supply or applying organic farming systems to agriculture will be unable to satisfy the joint requirements of increased yield and environmental sustainability,” the scientists added. “Increasing food production on limited land resources will rely on innovative agronomic practices coupled to the genetic improvement of crops.”
One of Schroeder’s research advances led to the discovery of a sodium metal transporter that plays a key role in protecting plants from salt stress, which causes major crop losses in irrigated fields, such as those in the California central valley. Agricultural scientists in Australia, headed by co-author Rana Munns and her colleagues, have now utilized this type of sodium transporter in breeding research to engineer wheat plants that are more tolerant to salt in the soil, boosting wheat yields by a whopping 25 percent in field trials. This recent development could be used to improve the salt tolerance of crops, so they can be grown on previously productive farmland with soil that now lies fallow.
Another recent discovery, headed by co-authors Emanuel Delhaize in Australia and Leon Kochian at Cornell University, opens up the potential to grow crops on the 30 percent of the earth’s acidic soils that are now unusable for agricultural production because acid soils have high concentrations of the toxic metal aluminum. “When soils are acidic, aluminum ions are freed in the soil, resulting in toxicity to the plant,” the scientists write. “Once in the soil solution, aluminum damages the root tips of susceptible plants and inhibits root growth, which impairs the uptake of water and nutrients.”
From their recent findings, the plant biologists now understand how transport proteins control processes that allow roots to tolerate toxic aluminum. By engineering crops to convert aluminum ions into a non-toxic form, they said, agricultural scientists can now turn these unusable or low-yielding acidic soils into astonishingly productive farmland to grow crops for food and biofuels.
Other recent transport protein developments described by the biologists have been shown to increase the storage of iron and zinc in food crops to improve their nutritive qualities. Research of co-author Dr. Mary-Lou Guerinot at the Superfund Research Center at Dartmouth College has contributed to discovery of the transport mechanisms for iron and zinc. “Over two billion people suffer from iron and zinc deficiencies because their plant-based diets are not a sufficiently rich source of these essential elements,” the biologists write.
The biologists said crops could be made more efficient in using water through discoveries in plant transport proteins that regulate the “stomatal pores” in the epidermis of leaves, where plants lose more than 90 percent of their water through transpiration. Two other major goals in agriculture are increasing the carbohydrate content and pest-resistance of crops. A recent discovery of protein transporters that move sugar throughout the plant has been used to develop rice plants that confer pest resistance to crops, the biologists said, providing a novel way to simplify the engineering of crops with high yields and pest resistance, which could lead to reduced use of pesticides in the field.
These recent developments in understanding the biology of plant transporters are leading to improved varieties less susceptible to adverse environments and for improving human health. Says Schroeder, “More fundamental knowledge and basic discovery research is needed and would enable us to further and fully exploit these advances and pursue new promising avenues of plant improvement in light of heavy metal containing soils and waters as well as increasing food and energy demands.”
In addition to Schroeder and Guerinot, the co-authors of the paper are Emmanuel Delhaize of CSIRO in Canberra, Australia; Wolf Frommer of the Carnegie Institution of Science; Mary LouGuerinot of Dartmouth College; Maria Harrison of the Boyce Thompson Institute for Plant Research in Ithaca, NY; Luis Herrera-Estrella of the Center for Research and Advanced Studies of the National Polytechnic Institute in Iraputo, Mexico; Tomoaki Horie of Shinshu University in Nagano, Japan; Leon Kochian of Cornell University; Rana Munns of the University of Western Australia in Perth; Naoko Nishizawa of Ishikawa Prefectural University in Japan; Dale Sanders of the John Innes Center in Norwich England; and Yi-Fang Tsay of the National Academy of Science of Taiwan.